If it was me I would get a clean urine sample from a friend and sub. Due to the timeline you may be able to get a synthetic sample to sub at a headshop locally. Follow the substitution sticky on how to sub properly. Now since you failed they may want you to give an observed sample so that could be a problem with subbing.
Since you haven't smoked much I think if you follow the dilution sticky to the letter you would probably pass. If I was in your spot I would get a clean sample for subbing and jock it and I would also do the dilution method as a backup. If for some reason you have to be observed due to the failure you can still have a damn good chance with dilution.
The one thing that bothers me about your story is that they said you failed the rapid strip barely. I was under the impression from reading various websites that any faint line showing up is a negative. Now if it was sent out for confirmation you may be high enough to fail. Let us know how you do, good luck.